1. Field of the Invention
The present invention relates generally to a wireless mobile communication system, and in particular, to an apparatus and method for a base transceiver station (BTS) to determine a priority for uplink scheduling of a mobile station in a wireless mobile communication system.
2. Description of the Related Art
Since a scheduling method is not used in an uplink of a conventional wireless mobile communication system, i.e., a Code Division Multiple Access (CDMA) communication system, priority does not have to be determined for mobile stations. Instead, using a transmission rate control method, interference control of the mobile stations is performed, and a data rate of each mobile station is determined. Herein, the transmission rate control method is a method of increasing or decreasing a data rate of all mobile stations en bloc according to the amount of interference in a cell. That is, a Base Transceiver Station (BTS) of a CDMA communication system controls data rates of mobile stations according to a variation of Rise over Thermal (RoT), which is a ratio of a sum of self-cell interference, other-cell interference, and thermal noise to the thermal noise so that transmission power of all mobile stations can reach the BTS as constant receive power regardless of distances between the BTS and the mobile stations.
In more detail, each BTS of the CDMA communication system measures a sum of signal interference (RoT) in a self-cell, signal interference from other cells, and thermal interference, and if the total interference exceeds a pre-set threshold, the BTS reduces the effect of signal interference by decreasing en bloc a data rate of mobile stations placed in the coverage thereof, and if the total interference does not exceed the pre-set threshold, the BTS increases the effect of signal interference by increasing en bloc the data rate of the mobile stations placed in the coverage thereof so that the amount of interference (RoT) in the self-cell is maintained within a predetermined range. This method is effective since most of the amount of interference of each BTS is signal interference in a self-cell in an uplink of the CDMA communication system. Because of this, the interference in a self-cell of the CDMA communication system can be directly controlled by controlling the data rate of all mobile stations in the cell. Thus, since interference of the entire communication system can be controlled by each BTS controlling only signal interference in a self-cell, a data rate of each mobile station can be guaranteed at a predetermined level.
However, in a broadband wireless access communication system or a 2.3 GHz portable Internet (WiBro) communication system based on the IEEE 802.16e standard, which has been developed and available on the market as a next generation mobile communication system, the method guaranteeing data rate cannot be applied according to a system characteristic. That is, since most of the amount of interference in an uplink of the system is signal interference from other cells, i.e., since interference in a self-cell can be ignored, it is difficult for each BTS to directly control the other cell interference as in the CDMA communication system.
Characteristics of the broadband wireless access communication system and the portable Internet communication system, which can be distinguished from the conventional CDMA communication system, will be described. Hereinafter, for convenience of description, the broadband wireless access communication system or the portable Internet communication system is called a WiBro communication system.
First, in the WiBro communication system, a BTS performs a ranging process between mobile stations so that signals transmitted from different mobile stations arrives at the BTS at the same time and controls each of the mobile stations to insert a cyclic prefix field into data bursts to be transmitted so that signals arriving at the BTS at different times through multiple paths do not interfere with each other. In addition, since the WiBro communication system uses the Orthogonal Frequency Division Multiple Access (OFDMA) scheme, orthogonality exists between subcarriers. Thus, a signal of a mobile station to which a specific slot is allocated does not interfere with a signal of another mobile station to which another slot is allocated.
Secondly, in the WiBro communication system, since an uplink is constituted with diversity subchannels, adjacent BTSs use different subchannels.
Based on the characteristic of the WiBro communication system, the transmission rate control method applied to the conventional CDMA communication system cannot be applied to the WiBro communication system. In addition, since a high transmission rate can be obtained for a mobile station located near a BTS using maximum transmission power, the scheduling method is more suitable for the mobile station located near the BTS than the transmission rate control method.